An image-forming material has a layer comprising a photopolymer. In general, a photopolymer changes its molecular structure by irradiation with light to increase or decrease its solubility in a kind of solvent to an appreciable extent. By taking advantage of this phenomenon, images can be formed in the photopolymer layer. Therefore, image-forming materials of such a kind are employed depending on the end-use purpose as printing plates, such as a presensitized plate, a resin relief plate, etc., photoresists such as dry film resist, a prepress color proof, a contact lithographic film, and so on in a wide field which requires visible images, covering from general photography to graphic arts and/or photomechanical processes.
For instance, when it is used for forming a colored image, the image-forming material has a construction such as to have on a support, in sequence, a coloring layer containing a coloring agent and a binder, and a photopolymer layer.
A coloring layer is obtained by coating a coloring matter dissolved or dispersed in an organic solvent on a support whose surface has been subjected to a surface treatment, and/or covered with a subbing layer, and drying the coating. In the coating and drying steps, it is essential by all means to make the coloring layer uniform in order to fully achieve properties of the image-forming material.
However, it has so far been very difficult to obtain a uniform colored layer in the drying step. This is because the drying has hitherto been carried out by blowing temperature- and humidity-regulated air against the colored matter coated on the support to evaporate the solvent, and the air stream and/or any disorder of the temperature- and humidity-regulated air used therein cause unevenness in the thickness distribution of the dried coloring layer.
Unevenness of the film thickness of the coloring layer causes not only a bad impression in appearance, but also non uniformity of density at the stages of exposure and development, and a lowering of reproducibility of an original image.
In order to prevent the unevenness, gentle drying is required. For instance, one method which has been carried out for this purpose involves blowing dried air against the coated layer at a very low speed taking a great deal of time in drying it up; another method involves letting drying air have a temperature gradient, that is to say, letting the drying air have a low temperature at the initial stage of drying and letting it have a high temperature at the latter stage; and a third method involves adding a solvent having a high boiling point to the solvent in which the coloring composition is dissolved or dispersed. However, even using such methods, it is difficult to prevent completely an uneven distribution of the film thickness from occurring due to the drying air. In addition, since a belt-shaped support is made to travel and thereon, a coloring composition is continuously coated and dried in the case of producing a image-forming material industrially, such methods necessitate huge and complicated drying equipment. Further, a selection of solvent required in those methods imposes great restrictions on selection of ingredients themselves to constitute the coloring layer.